In the completion of wells drilled into subterranean formations, a casing string is normally run into the well and cemented to the wall of the well. Then perforating guns are used to create perforation tunnels through the casing. The perforation tunnels are created adjacent the formation at pay zones to allow fluids, such as oil or gas, to flow from the formation into the well.
During the well completion phase, a fracture operation may be used to increase the permeability of the formation. A fracture operation typically involves lowering a work string to a point adjacent the formation to be fractured, i.e. near the perforation tunnels. Then fracturing fluid is pumped out of the lower end of the work string and into the perforation tunnels at a pressure sufficient to cause the bedding planes of the formation to separate. This separation of the bedding planes creates a network of permeable fractures through which formation fluid can flow into the well after completion of the fracture operation.
The fractures have a tendency to close once the fracture pressure is relaxed. Thus, proppants (e.g. sand, gravel, or other particulate material) are routinely mixed with the fracturing fluid to form a slurry which carries the proppants into the fractures where they remain to prop the fractures open when the pressure is reduced. A condition referred to as screen-out may occur when a portion of the proppants comes out of the perforation tunnels and fills up the annular space between the casing and the work string. Screen-out can occur more than once during a fracture operation.
Whenever screen-out occurs or after the fracture operation is completed, it is necessary to circulate the fracturing fluid out of the work string. Typically, a mechanical valve with multiple open/close capability is required to permit circulation of the fracturing fluid out of the work string.
In general, in one aspect, the invention features a valve for use in a tool positioned in a well that includes a body having a bore and a port connected to permit fluid communication between the well and the bore. A piston is supported in the body for movement between an open position to open the port and a closed position to close the port. A rupture disc is responsive to fluid pressure in the well and ruptures when a predetermined pressure is applied so that fluid pressure is communicated to the piston to move it from the closed position to the open position. A lock member secures the piston in the closed position after the piston moves from the open position to the closed position.
Other features will become apparent from the following claims.